Primary care is fundamentally about a long-term relationship between a person and their clinician, who provides care for most of their health needs and coordinates additional health care for services beyond their area of expertise. The Institute of Medicine gave this definition for primary care in 1996: "Primary care is the provision of integrated, accessible health care services by clinicians who are accountable for addressing a large majority of personal health care needs, developing a sustained partnership with patients, and practicing in the context of family and community."

Primary care may also be thought of as a level of care in the larger health care system, to be distinguished from secondary care (care provided by community-based specialists and local community hospitals) and tertiary care (care provided by specialists at regional or academic health centers). In non-industrialized nations with limited health resources, primary care may be provided by village health workers, nurse-auxiliaires, promotoras, community health advisors, barefoot-doctors, etc. In this context, physicians would be a scarce enough resource to qualify as secondary care, while regional hospitals might represent tertiary care. The World Health Organization provided a definition of primary care useful in this context during the Alma Ata Conference of 1978:

"Primary health care is essential health care ... made universally accessible to individuals and families in the community ... through their full participation and at a cost that the community and country can afford."

Who practices primary care?

Both allopathic (M.D.) and osteopathic physicians (D.O.) in the disciplines of family practice, general internal medicine, and general pediatrics are universally acknowledged as primary care clinicians. Nurse practitioners (NPs, also known as Advanced-Practice Nurses) and physician assistants (PAs) practicing in these disciplines are also primary care clinicians. Physicians without residency training in a primary care discipline may also practice primary care as GP's (general practitioners). Specialists in preventive medicine are sometimes also listed as primary care clinicians, although these may consider the community to be their "patient".